1. Field of the Invention
The present invention relates to a novel silicone type cinnamic acid derivative and a method of preparing same, and to a novel UV-ray absorber and an external skin treatment agent.
More specifically, the present invention relates to a novel silicone type cinnamic acid derivative which can be dissolved in silicone oil, has an excellent water resistance and oil resistance, and has an UV-ray absorbing characteristic at wavelengths in the UV-B region, and to a novel external treatment agent having an excellent sunburn-prevention effect, useability, and prolonged cosmetic effects.
2. Description of the Related Art
As is well known, UV-rays cause various changes to the skin, and dermatologically, the acting wavelengths thereof are classified into long wavelength UV-rays of 400 to 320 nm, medium wavelength UV-rays of 320 to 290 nm, and short wavelength UV-rays shorter than 290 nm; called UV-A, UV-B, and UV-C, respectively.
Generally, most of the UV-rays to which humans are exposed are sunlight rays, and consist of UV-rays reaching the earth, i.e., UV-A and UV-B, and UV-rays absorbed in the ozone layer and not reaching the earth, i.e., UV-C. Of the UV-rays reaching the earth, UV-B rays cause erythema or blistering when irradiated on the skin at a certain dose or higher, and further, promote the forming of melanine in the skin, i.e., cause a darkening or dyeing of the skin.
Accordingly, protection of the skin from UV-B rays is very important from the viewpoint of preventing an accelerated aging of the skin and a generation or increase of splotching or freckling of the skin, and thus various UV-B absorbers to be used for this purpose have been developed.
Among existing UV-B absorbers, there are known PABA derivatives, cinnamic acid derivatives, salicylic acid derivatives, camphor derivatives, urocannic acid derivatives, benzophenone derivatives, and heterocyclic derivatives, and these UV-B absorbers are utilized exclusively by formulation in external treatment agents such as cosmetics and quasi-drugs.
As the external agent bases, silicone type bases with low molecular weights, such as dimethylsiloxane, are widely used, as is well known in the art, due to the excellent useability characteristics of such silicone type bases, e.g., a good extendability, plain feeling, and no stickiness, and an excellent function thereof in that they are not easily removed by sweat or water.
On the other hand, since sun-protection cosmetics in which UV-ray absorbers are formulated are used during hot summer, they are liable to be removed by excessive sweating or skin fat extrusions, and when these products are used at the beach or at a swimming pool, a problem arises in that they are removed when the skin is immersed in water. Therefore, there is obviously a need to enhance the cosmetic durability of these cosmetics, and accordingly, a silicone type base with a low molecular weight such as dimethylsiloxane, etc., is now widely used as the external treatment agent base, due in the most part to the properties possessed by silicone type bases; for example, a useability such as good spreadability, a plain feeling, no stickiness, and further, functional characteristics such as an excellent water resistance, oil resistance, and resistance to easy removal by sweat or water.
Nevertheless, existing UV-B absorbers have a remarkably low compatibility with or low solubility in silicone type bases, and accordingly, to formulate such UV-B absorbers in an external treatment agent having a silicone type base, an oily base must be added, and therefore, a drawback arises in that the useful properties of the silicon type base as described above are lost, and further, these compositions have an inferior water resistance and oil resistance.
Japanese Examined Patent Publication (Kokoku) No. 29866/1969, Japanese Unexamined Patent Publications (Kokai) Nos. 58991/1985 and 108431/1985 disclose compositions having a UV-ray absorbability, but the chemical structures thereof include unsubstituted cinnamic acid as the basic skeleton, which has an absorption maximum wavelength on the UV-C side, in silicone oil, and thus the UV-B absorbability thereof is not satisfactory. FIG. 3 shows the UV absorption spectrum of 3-bis(trimethysiloxy)-methylsilyl-2-methylpropyl-cinnamate, from which it can be understood that this composition does not have an adequate wavelength region for a UV-B absorber.